1. Field of the Invention
The present invention relates to an apparatus for reproducing symbol signals which are time-division-multiplexed with a video signal during the vertical blanking interval of the video signal, as symbol data on a television receiver (hereinafter referred to as TV receiver).
2. Description of the Prior Art
Heretofore, in the case of superposition of symbol information on a picture of the TV receiver, the symbol data is either reproduced in the color green or in full color and video signals whose display corresponds to the time the video forms a background for the superposed symbol data are erased and replaced with a suitable uniform color; or the video signal level during this time and the symbol signals are given as multiplex signals.
In the latter method, when the video data of the TV signal serving as the background of the superposed symbols includes white peak symbols such as time symbols or a commercial message, even though the symbol data given by the multiplex signals is superposed on it, two kinds of symbol data are superposed with each other whereby the symbol data can not be read out.
In the former case, there is no such problem, however, since the video data at the part for superposing the symbol data is disadvantageously erased. With regard to the erasing time, in the case that the symbol size is 36 vertical lines by 2 rows at 48 lines per row as the horizontal scanning line number, the total number of scanning lines for the multiplex time of the symbol signal is 96.
In the case that the upper and lower spaces require 20 lines respectively, the total number of scanning lines for the multiplex time is 136 which corresponds to about 1/3 of the total effective scanning lines of 435 lines on the picture of TV receiver. (The total number of scanning lines is 525, the number of scanning lines for the vertical blanking interval is 42 and the number of scanning lines for 10% over scan is 48). Accordingly, about 1/3 of the video signal is erased in the latter superposing method.
When broadcasting contents are decided under the consideration of the erasing time, the broadcasting contents are highly affected by the superposing time.